Respiratory frequency and tidal volume during exercise: differential control and unbalanced interdependence

Area of Science:

• Exercise Physiology
• Respiratory Control
• Human Performance

Background:

• Exercise hyperpnoea regulation is complex, with respiratory frequency (f_R) and tidal volume (V_T) potentially controlled by distinct physiological inputs.
• Understanding the independent and interdependent regulation of f_R and V_T is crucial for advancing knowledge of breathing during physical activity.

Purpose of the Study:

• To investigate the differential regulation of respiratory frequency (f_R) and tidal volume (V_T) during various exercise protocols.
• To elucidate the relationship between f_R, V_T, and other physiological and perceptual variables during exercise.

Main Methods:

• Twelve cyclists completed an incremental test and three randomized experimental sessions involving sinusoidal and self-paced trapezoidal workload manipulations.
• Exercise intensity and duration were varied using sinusoidal protocols (2-min and 8-min periods) and a self-paced trapezoidal rating of perceived exertion (RPE) protocol.

Main Results:

• Respiratory frequency (f_R) demonstrated a stronger association with RPE than with workload, gas exchange, V_T, or muscle activation.
• f_R dissociated from RPE during moderate exercise intensity.
• Tidal volume (V_T) and minute ventilation (V̇_E) exhibited similar temporal patterns and high correlation; V_T appeared to adjust based on f_R to meet V̇_E demands.

Conclusions:

• Respiratory frequency (f_R) is primarily driven by perceived exertion (RPE) rather than mechanical or metabolic factors during exercise.
• Tidal volume (V_T) dynamically adjusts to respiratory frequency (f_R) to achieve target minute ventilation (V̇_E), highlighting an unbalanced interdependence.
• These findings offer a new framework for understanding the mechanisms of exercise hyperpnoea and the control of breathing during physical exertion.